Sensor-based strategies for accurate prediction of drilled hole surface integrity of CFRP/Al7075 hybrid stack

Abstract

The airplane structure is often made up using carbon fiber reinforced plastic (CFRP) stacking with a metallic sheet to improve excessive load carrying and shock-absorbing capability with reduced fuel economy. It is a challenging task to drill dissimilar CFRP-Al metallic stack because the hot continuous metallic chip mutilates the hole surface in addition to drilling-induced delamination. The present work addresses the parametric effect on delamination, roughness, and circularity error of the drilled hole along with chip morphology using different drill geometry on the fabricated CFRP [0°/-45°/90°/45°]2s stack over an aluminum 7075 sheet. A drill tool dynamometer was used to capture axial thrust with associated torque variations during drilling which were further used in process monitoring. The most critical unlike interface drilling has been scrutinized using instantaneous force-torque slopes along with scanning electron micrographs. The machining time loss during CFRP→Al interface drilling has also been processed. Finally, a comparative assessment has been made on the predictability of hole quality features among various sensor-based strategies using response surface methodology. The drilled-hole surface quality was significantly improved at high spindle speed (2250 rpm), and low feed rate (0.025 mm/rev) using a low drill point angle (110°). The thrust force was found to be a prime indicator of drilled hole integrity than torque whereas peak torque and its slope in the initial stages of the drilling cycle strongly correlated with surface delamination. The top surface delamination was somewhat severe (≥ 1.6) at high drill thrust (≥ 40 N) with high torque (≥ 0.45 Nm).